This invention results from a need to improve octane ratings for gasoline. Isoparaffin-olefin alkylation is a means to produce highly branched paraffins which affect this octane improvement.
Alkylation is a reaction in which an alkyl group is added to an organic molecule. Thus, an isoparaffin can be reacted with an olefin to provide an isoparaffin of higher molecular weight. Industrially, the concept depends on the reaction of a C.sub.2 to C.sub.5 olefin with isobutane in the presence of an acidic catalyst producing a so-called alkylate, a valuable blending component in the manufacture of gasolines because of its high octane rating.
Traditionally, the process in the industry includes the use of hydrofluoric acid or sulfuric acid as a catalyst carried out under controlled temperature conditions. Low temperatures are utilized in the sulfuric acid process to minimize the side reaction of olefin polymerization and the acid strength is generally maintained at 88 to 94% by the continuous addition of fresh acid and the continuous withdrawal of spent acid. The hydrofluoric acid process is less temperature-sensitive and the acid is easily recovered and purified.
The typical types of alkylation currently used to produce high octane blending components, that is, the hydrofluoric acid and sulfuric acid alkylation processes, have inherent drawbacks including environmental concerns, acid consumption and sludge disposal. With the increasing demands for octane and the increasing environmental concerns, it has been desirable to develop an alkylation process based on a catalyst system which can meet product quality demands, while at the same time minimizing safety and environmental problems.
U.S. Pat. No. 3,644,565 discloses alkylation of a paraffin with an olefin in the presence of a catalyst comprising a Group VIII noble metal present on a crystalline aluminosilicate zeolite. The catalyst is pretreated with hydrogen to promote selectivity.
U.S. Pat. No. 3,647,916 describes an isoparaffin-olefin alkylation process featuring use of an ion-exchanged crystalline aluminosilicate, isoparaffin/olefin molar ratios below 3:1 and regeneration of the catalyst.
U.S. Pat. No. 3,655,813 discloses a process for alkylating C.sub.4 -C.sub.5 isoparaffins with C.sub.3 -C.sub.9 olefins using a crystalline aluminosilicate zeolite catalyst wherein a halide adjuvant is used in the alkylation reactor. The isoparaffin and olefin are introduced into the alkylation reactor at specified concentrations and catalyst is continuously regenerated outside the alkylation reactor.
U.S. Pat. No. 3,236,671 discloses an alkylation reaction wherein crystalline aluminosilicate zeolites having silica to alumina mole ratios above 3 are used. The reference also discloses the use of various metals exchanged and/or impregnated on such zeolites.
U.S. Pat. No. 3,738,977 discloses alkylation of paraffins with ethylene using a zeolite catalyst which possesses a Group VII metal component. The catalyst is pretreated with hydrogen.
U.S. Pat. No. 3,917,738 describes a process for alkylating an isoparaffin with an olefin using a solid, particulate catalyst capable of absorbing the olefin. The isoparaffin and the olefin are admixed to form a reactant stream in contact with catalyst particles at the upstream end of an adsorption zone. Thereafter, the reactants are passed concurrently with the catalyst so that a controlled amount of olefin is adsorbed into the catalyst before the combination of reactants and catalyst is introduced into an alkylation zone. This controlled olefin adsorption is thought to prevent polymerization of the olefin during alkyation.
U.S. Pat. No. 4,384,161 describes a process of alkylating isoparaffins with olefins to provide alkylate using a large-pore zeolite catalyst capable of absorbing 2,2,4-trimethylpentane, for example, ZSM-4, ZSM-20, ZSM-3, ZSM-18, zeolite Beta, faujasite, mordenite, zeolite Y and the rare earth metal-containing forms thereof, and a Lewis acid such as boron trifluoride, antimony pentafluoride or aluminum trichloride. The use of a large-pore zeolite with a Lewis acid is reported to increase the activity and selectivity of the zeolite, thereby effecting alkylation with high olefin space velocity and low isoparaffin:olefin ratio.
In the past, severe activity and stability problems have been noted with respect to zeolite-based alkylation catalyst systems. U.S. Pat. Nos. 3,251,902 and 3,893,942, as well as French Patent 1,593,716, and the article by Kirsh and Potts, Div. of Pet. Chem. A.C.S., 15, A109 (1970), exemplify these problems. Improved stability was noted when a Lewis acid such as BF.sub.3 was used in combination with macroreticular acid cation exchange resins as pointed out in U.S. Pat. No. 3,855,342. More recently, U.S. Pat. No. 4,384,161 has disclosed the use of BF.sub.3 in combination with large pore zeolites such as ZSM-4 and Beta to effectively catalyze isoparaffin/olefin alkylation reactions.
U.S. Pat. No. 3,467,728 relates to a process for isomerizing olefinic hydrocarbon, such as 1-butene or 1-pentene, by contacting the hydrocarbon with a catalyst comprising a crystalline alumina silicate combined with a substantially anhydrous boron halide.
The two-part article, "Modern Alkylation", by Lyle F. Albright, Oil and Gas Journal, Nov. 12 and 26, 1990, summarizes the state of the art in alkylation technology, and highlights problems associated with various liquid catalyst systems, further emphasizing the desirability of developing a commercially viable isoparaffin/olefin alkylation process employing a promoted solid catalyst.
U.S. Pat. No. 5,191,148 to Degnan et al. teaches a process for alkylating an isoparaffin with an olefin in the presence of a synthetic porous material designated as MCM-41. Each of the preceeding references is incorporated by reference as if set forth at length herein.